My experience showed me that you should not trust these tools completely. Take your javascript, run it through compressor and put it back to your application to see if it use. Most of those online tools made few errors here and there. Commercial tool SOC did the job without any error.

3. gzip response. This is widely used and almost a must in all today’s applications. Usually you would configure your webserver for this (Apache mod_gzip or for Tomcat compresion=”onî in server.xml), but you can do it also over servlet filter.
Here is one that works – download gzip.rar.

All these things reduced my .js size by more then 60% and that is a huge win.